Zapping from a channel to another channel usually takes some time, typically between 1.5 and 2.5 seconds in a broadcast television environment. This time is typically made up of                Identifying technical setting (transport stream locations, frequency, etc.);        Tuning to the new frequency (if required);        Starting descrambling (if required);        Acquiring the first key frame (i-frame) in the stream to start decoding;        Controlling parental criteria for the program; etc.        
On most broadcast television platforms, the zapping sequence is experienced by the user as a “black screen”, i.e. no video and no audio. Sometimes the user is presented with a zap banner showing the name of the next channel and information about the current program of this next channel.
Some alternative user experiences have previously been tested or deployed on some broadcast platforms or in laboratories where the black screen is replaced by a colored screen, or pictures with or without animations, or a video of the channel's logo.
In parallel a lot of effort has previously been deployed to reduce the channel change time, e.g. by reordering the different steps of the process, prioritizing tasks, using multi-picture-in-picture, etc.
There have also been some efforts made to avoid the “black screen” in general (not only for zapping) by filling the time gap with appropriate video. For example, United States patent publication US 2008/0044161 describes how to switch smoothly between compressed videos by using a pre-recorded uncompressed copy of one of the videos; United States patent publication US 2008/0282285 describes how to play alternative content while the user is pausing the current media in review buffer; and United Kingdom patent GB 2 302 635 describes how to play a special one-to-all video while the user is controlling one-to-one content with idle time or non-transmission time in a Video-On-Demand (VOD) infrastructure